In multi-cylinder internal combustion engines, varying the timing of the fuel supplied to the various cylinder injectors has a significant impact on the operating efficiency of the engine. Heretofore various systems have been utilized to effect the desired timing variations; however, such systems have been beset with one or more of the following shortcomings: (a) they were of a costly and complex construction; (b) they were highly susceptible to malfunction and required an inordinate amount of maintenance and service by a skilled mechanic; (c) various components of the systems were subjected to excessive wear; and (d) each of the systems embodied an inordinate number of components making the installation thereof on the engine an awkward, frustrating and time-consuming operation.